Why ASP.NET webmethod returns 500 when query string parameters are passed

I have the following webmethod:

[WebMethod(true)]
[ScriptMethod(UseHttpGet = true, ResponseFormat = ResponseFormat.Json)]
public static String requestLocalCrime(string lat, string lng)
{
    try
    {
        // Initialize the WebRequest.

        String LocalCrime = "http://policeapi2.rkh.co.uk/api/crimes-street/all-crime?lat=" + lat + "&lng=" + lng + "";

        WebRequest webRequest;
        WebResponse webResponse;

        webRequest = HttpWebRequest.Create(LocalCrime) as HttpWebRequest;
        webRequest.Method = WebRequestMethods.Http.Get;
        webRequest.ContentType = "application/json; charset=utf-8";
        Encoding encode = System.Text.Encoding.GetEncoding("utf-8");

        webRequest.Credentials = new NetworkCredential(
                ConfigurationManager.AppSettings["PoliceAPIUsername"].ToString(),
                ConfigurationManager.AppSettings["PoliceAPIPassword"].ToString());

        // Return the response. 
        webResponse = webRequest.GetResponse();

        using (StreamReader reader = new StreamReader(webResponse.GetResponseStream(), encode))

        {
            string results = reader.ReadToEnd();
            reader.Close();
            webResponse.Close();
            return results;
        }


    }
    catch(Exception e) {
        return e.Message;
    }
}

which I am calling via jQuery:

 var params = {
            "lat": 50.819522,
            "lng": -0.13642
        }


$.ajax({
            type: "GET",
            contentType: "application/json; charset=utf-8",
            data: JSON.stringify({ "lat": params.lat, "lng": params.lng }),
            url: "crimerequest.aspx/requestLocalCrime",
            dataType: "json",
            // success: insertCallback 
            success: function (data) {
                var result = $.parseJSON(data.d);
            },
            error: function (xhr, ajaxOptions, thrownError) {
                alert(xhr.status);  // Returns 500
                alert(thrownError); // Internal Server Error
                return false;
            }
        });

the problem is the current LocalCrime string breaks with a 500 but if I replace it with:

String LocalCrime = "http://policeapi2.rkh.co.uk/api/leicestershire/C01/crime"

Then suddenly without the query string values it works.

Any help is much appreciated.

Okay I wrote a proxy class so I can debug now. return results; does bring back what I want but it is inside an array, maybe that has to do with it. my data looks like this (probably something in the client side is getting this data wrong):

[
{
    "category": "other-crime", 
    "id": 378815, 
    "location": {
        "latitude": "50.8188090", 
        "street": {
            "id": 379, 
            "name": "On or near Abbey Road"
        }, 
        "longitude": "-0.1196796"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "anti-social-behaviour", 
    "id": 377906, 
    "location": {
        "latitude": "50.8279907", 
        "street": {
            "id": 4721, 
            "name": "On or near Albion Street"
        }, 
        "longitude": "-0.1336384"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "anti-social-behaviour", 
    "id": 377849, 
    "location": {
        "latitude": "50.8279907", 
  开发者_JAVA技巧      "street": {
            "id": 4721, 
            "name": "On or near Albion Street"
        }, 
        "longitude": "-0.1336384"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "other-crime", 
    "id": 377801, 
    "location": {
        "latitude": "50.8279907", 
        "street": {
            "id": 4721, 
            "name": "On or near Albion Street"
        }, 
        "longitude": "-0.1336384"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "burglary", 
    "id": 377781, 
    "location": {
        "latitude": "50.8279907", 
        "street": {
            "id": 4721, 
            "name": "On or near Albion Street"
        }, 
        "longitude": "-0.1336384"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "vehicle-crime", 
    "id": 376569, 
    "location": {
        "latitude": "50.8279446", 
        "street": {
            "id": 6312, 
            "name": "On or near Alexandra Villas"
        }, 
        "longitude": "-0.1454119"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "anti-social-behaviour", 
    "id": 376525, 
    "location": {
        "latitude": "50.8279446", 
        "street": {
            "id": 6312, 
            "name": "On or near Alexandra Villas"
        }, 
        "longitude": "-0.1454119"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "anti-social-behaviour", 
    "id": 376519, 
    "location": {
        "latitude": "50.8279446", 
        "street": {
            "id": 6312, 
            "name": "On or near Alexandra Villas"
        }, 
        "longitude": "-0.1454119"
    }, 
    "context": "", 
    "month": "2011-04"
}, 
{
    "category": "anti-social-behaviour", 
    "id": 376518, 
    "location": {
        "latitude": "50.8279446", 
        "street": {
            "id": 6312, 
            "name": "On or near Alexandra Villas"
        }, 
        "longitude": "-0.1454119"
    }, 
    "context": "", 
    "month": "2011-04"
}
]

The query string parameters need to be passed as JSON. You are not passing them correctly so I guess lat and long are null in your web method. To pass them correctly use the following:

data: JSON.stringify({ "lat": params.lat, "lng": params.lng })

The JSON.stringify method is natively implemented in modern browsers. If you need to maintain legacy browsers you might need to include json2.js script which will use the native method if the browser supports it and if not use its implementation.

Also note that your web method returns a plain string. This means that on the client data.d will be a string. If you want to manipulate it as an object you will need to parse it first:

var result = $.parseJSON(data.d);

If you are getting this error, this means you are conceptually doing wrong somewhere.Ideally ajax scenarios are meant only for small to medium server side calls not for getting tons of data, and if you are getting a lot of data using the asynchronous request then you are asking for trouble.So in such scenarios it is best to go and implement server side logic.But what if you are at a stage where you can't change your application logic now add this to your web.config:

<system.web.extensions>
<scripting>
<webServices>
<jsonSerialization maxJsonLength="2147483644"></jsonSerialization>
</webServices>
</scripting>
</system.web.extensions>

Important thing to keep in mind is that the maximum value for the integer field is 2147483647 and this limit has to remain inside the bounds of this value.

But now I am really worried as I need this app to be scalable for heavy use. I made this work but please let me know how can I improve my practice. Thank you